# 列表记录学生的年龄
my_list = [21,25,21,23,22,20]

my_list.append(31)
print(my_list)

my_list.extend([29,33,30])
print(my_list)

my_list.remove(21)
print(my_list)

my_list.remove(30)
print(my_list)

index = my_list.index(31)
print(index)